METHODS USED AND RESULTS OBTAINED IN THE TRANSFORMATION OF SHEEP BREEDING IN THE PEOPLE'S REPUBLIC OF BULGARIA

Ts. Hinkovski, A. Stoyanov, V. Lazarov, L. Mihaiiova, Sv. Raichev

INTRODUCTION

The People's Republic of Bulgaria ranks among the first countries in the world in terms of number of sheep and amount of sheep produced per one hundred hectares of arable land and per capita. Radical changes have taken place in this country's sheep breeding over the past thirty-five years. Prior to World War Two the breeds used were of coarse and semi-coarse wool types, yielding low amounts. As high as 64.5 per cent of the sheep in Bulgaria belonged to unidentified breeds and were predominantly crosses between aboriginal breeds. Of the indigenous sheep the Karnobat-Shoumenska breed (22.2% ) accounted for the highest proportion.

At present, sheep of newly developed fine wool, semi-fine wool and local coarse wool breeds are raised in the People's Republic of Bulgaria. On a national scale with regard to the number of sheep that were raised in this country in 1982 fine wool breeds accounted for the highest proportion (41% ), followed by the Tsigai sheep (25.3% ) and the semifine-wool breeds (16.7% ).It is envisaged that the number of specialised milk sheep will increase in the near future as against a slight decline in the number of fine wool and semi-fine wool sheep.

There has been a large increase in the amount of wool and meat produced and to a lesser extent in the output of sheep milk during the 1939 – 1982 period. The production of wool rose 2.8times and the production of sheep meat increased by 90 per cent, while that of sheep milk rose by 10 per cent.

PERFORMANCE RESULTS

Bulgaria is one of the few countries in the world, and the only one in Europe that meets the needs of its well developed wool-textile industy with wool of its own production. This is the result of the proper structure of sheep breeding, in compliance with the demands of the country, and of a unified programme concerning the breed transformation of the sheep population on a national scale. Research teams of outstanding scientists, experts, and practitioners were assigned the task of leading the work in this respect. In a comparatively short time as many as four fine wool breeds were developed in the lowland regions of this country, and two semifine-wool breeds and two Tsigai-type breeds will shortly be developed for the semimountainous and mountainous regions. A specialized milk breed is also in the course of development.

Agricultural Academy of the People's Republic of Bulgaria, Suhodolska Str., 30, Sofia, Bulgaria.

The method of multiple reproductive crossbreeding was the basic one to be employed in the transformation of sheep breeding - aboriginal sheep were mated with rams of breeds that were imported from the USSR and the German Democratic Republic. The main breeds that were used as improvers in fine-wool breeding were Mutton Merino, Caucasian, Askania and Stavropol; in semifine-wool breeding the North Caucasian was used and in recent years Corriedale, imported from New Zealand and Australia, has also been used. Tsigai sheep breeding was developed on the base of the Tsigai breed. The programmes that were worked out beforehand for breed development were theoretically substantiated and applied in compliance with the quality of the initial populations and with the ecologic conditions.

With the fine-wool breeds the desired selection type was most frequently reached in F₃ after which inbreeding was practised. In individual cases only inbreeding was shown to start in F₂. In the first stage of breed development semi-fine-wool sheep were created through crossing the local sheep with fine-wool rams. In the second stage the resulting merino-like sheep were mated with rams of the North Caucasian breed and with Corriedale rams. Romney Marsh and Lincoln rams were used on a limited scale. The desired crossbred type of sheep were produced most frequently with animals having 3/4 blood of breeds obtained through crossbreeding.

In the development of Tsigai sheep breeding a higher generation of crosses was reached with a view to equating the wool of a given type and obtaining higher productivity with the sheep in the mountainous regions.

The selection of sheep for various purposes at the Agro-Industrial Complexes and recording their performance are now carried out by the Animal Selection Centres, established in all districts of the country. A pedigree structure is built in all populations, including nearly 16% elite, 61% reproductive, and 23% stock flocks. Particular attention is paid in this country to the wool performance of sheep. That is why it is referred to as a fundamental selection character with sheep for all purposes except for those bred for milk.

Although the wool yielding capacity of sheep is genetically highly determined, it varies largely on a year-to-year basis under the effect of the environment. Over the 1970 – 1984 period the average wool yield from the elite part of the fine-wool population has varied from 6.1to 6.9kg, while that obtained from the semi fine-wooled and the Tsigai population has varied from 4.1to 4.3kg, and from 3.1to 3.3 kg, respectively.

The wool yielding capacity of ewes in the ram producing flocks has been considerably higher (Table 1). For the 1980 – 1984 period the amount of grease wool with the fine-wool breeds has been from 6.42 kg for Dounavska breed up to 7.73kg for the Northeast Bulgarian one, and the amount of scoured wool has ranged from 3.02 to 3.50 kg. On individual cooperative farms, such as Sadievo and Samouilovo (District of Sliven) and Kochovo (District of Shoumen) an exclusively high yield of wool has been obtained - 9.8kg per ewe, on an average. The record amounts with individual animals have reached 15.0kg. With semifine-wool breeds the amount of scoured wool per animal has ranged from 2.7to 2.8kg. With Tsigai sheep it has been from 2.4to 2.7kg.

The ewes of the elite part of the populations have good length of the staple. For the 1980 – 1983 period it has varied from 8.6to 9.1cm for the finewooled populations, from 9.2to 10.7cm for the semifine-wool populations, and from 9.8to 10.0cm for the Tsigai populations.

With regard to wool quality of fine-wool sheep 45.7 percent of the yield is of 70s and 64s, and 51.35 percent of 60s.

It is known that the quality of the young generation of rams used is of great importance for the genetic progress of the populations. In 1984 as many as 10,000 young fine-wool, semi fine-wool and Tsigai rams were used chiefly for artificial insemination in the flocks of the Agro-Industrial Complexes. They had comparatively high productivity (Table 2).The liveweight of the young rams belonging to the fine-wool breeds imported from the Soviet Union, but raised in this country, varies within the 94 – 99 kg range, while that of the young rams of the Bulgarian fine-wooled breeds is highest, ranging from 100 to 104 kg. The live weight of the semifine-wool young rams is from 91 to 93 kg, and that of the Tsigai young rams - from 80 to 84 kg.

The wool productivity of the young rams is high. At the age of 18 months the fine-wool rams have yielded more than 13.3kg, on an average, of greasy wool. Karnobatska fine-wool rams produce 16.2kg. The respective amounts of scoured wool per head have been more than 5.6kg, and 7.1kg (Karnobatska). The quantity of scoured wool is also high with the semifine-wool breeds giving 5.6and 6.5kg. With individual animals the maximum amount of 10.66kg has been obtained.

The precocity of animals has steadily been given due consideration in the process of selection and development with regard to all Bulgarian breeds. At equal properties and qualities only those of the animals with a high liveweight at weaning are kept for breeding. With the fine-wool and the Tsigai breed the live weight of the lambs at weaning equals 46% of the weight of adult sheep, and with the semifine-wool breed it is 45%.

The information obtained by the regular recording of productivity in the elite and the reproductive part of the populations shows that the sheep of all breeds are distinguished by high liveweight. At the age of 2.5years in 1980 the finewooled ewes weighed 61.3kg, the semi-finewooled ones - 55.8 kg, and Tsigai ones - 49.6 kg.

The assessment of the Bulgarian fine-wool breeds at competitions has shown that at fattening the lambs exhibit a good growth rate and good feed conversion (Table 3).The average daily gain with the individual breeds varies from 272 to 305 g. The food intake (fodder units) per kg gain ranges from 4.44 to 4.96, and that of digestible protein from 349.8 to 361.0g.

The fattened fine-wool lambs have been shown to have good meat performance. Depending on the breed the portion of meat in the carcass is from 58.6% to 60.6%, that of bone from 19.4to 22.0%, and that of fat from 6.6to 9.2%.

Comparatively good fertility of sheep has been reached in overcoming the low fertility of the indigenous breeds in the process of developing the new fine-wool and semifine-wool breeds. Records kept on a mass scale, with sheep of the elite part of the populations, reveal that with the fine-wool breeds fertility rates vary on a year-to-year basis within the range 119.6to 129.1per cent; with the semifine-wool breeds they vary from 105.0to 116.3per cent; and with the Tsigai sheep they are from 104.2 to 106.0 per cent. On individual farms of the Agro-Industrial Complexes where the animals are raised under very good conditions fertility rate varies from 130.0 to 140.0 per cent.

It is known that from time immemorial the sheep in Bulgaria were used as dairy animals, the milk obtained being processed into white brine cheese, kashkaval (yellow cheese), and sour milk (not to be confused with yoghurt) which have invariably been traditional foods for the Bulgarian people. Records on milk production in the elite flocks of the populations has shown that, depending on the year, 68.7 to 70.6 litres of milk (lactational capacity) are obtainable for a 120 day lactation with the fine-wool breeds. In the period following the weaning of lambs 37.0to 44.1 litres of milk is produced by a ewe, on an average. With the semifine-wool breeds the milk yielding capacity is higher - up to 52.0 litres per ewe.

At the present stage of purebreed reproduction with fine-wool sheep the main source of genetic progress is the selection carried out. In the elite part of the breeds the pairs for mating are chosen Individually, chiefly on the basis of progeny testing of the rams or their sons. The selection of sheep in the nucleus flocks of the breeds is carried out at five age levels - one month, 100 days, 6 months, 16 months, and 2.5years (by reproductive qualities).

Five Stations for testing the breeding value of rams are working now in this country. Nearly 15,000 newly produced young rams are annually studied in terms of wool yield and fineness via the employment of objective methods. With the progeny testing of rams records are kept of the productivity of their offspring at the ages of 6 and 16 months.

A considerable number of characters constitute the subject of selection with sheep. In the case of dual-purpose animals (wool and meat) and for the fine-wool, semifine-wool, and Tsigai type sheep the selection traits are graded in significance as follows: most important - scoured wool yield; important - liveweight at 100 days and 18 months of age, fertility, and wool length; while traits under observation include fibre diameter, fleece density, wool whiteness, and staple crimp. With the rams and the ram-producing ewes due consideration is given to the scoured fleece, while with the remaining types of sheep records are kept of the greasy wool.

The great number of selection characteristics limits the effect of each of them, however, it makes possible the overall improvement of the performance qualities of sheep, though at a slower pace.

SIMULATION RESULTS

Parallel to the accomplishments of practical selection, research is going on with regard to the maximisation of genetic progress and to raising the response to selection that follows different patterns. The prevailing values of coefficients as established by various authors for the most important heritable character-wool yield - are within the 0.3 to 0.5range, and for the inheritance of the live weight quality they are from 0.1to 0.4.

The value of genetic progress is studied by simulated selection on the base of real data for certain breeds. Table 4 reflects a selection index composed of seven characters used by Hinkovski (1971) with the Askania breed. Highest is the economic value of two characters: number of offsprings at the age of 2.5years, and wool yielding capacity at the age of 18 months. As the result of selection carried out by this index with 30 per cent of the ewes the highest genetic progress per generation has been obtained for the quantity of milk and the number of offspring, at 2.5years as well as for the liveweight at weaning (from 4.8up to 6.7 per cent). A comparatively good selection effect has also been produced with the wool yield (3.4 per cent). In other words, an overall upgrading effect is recorded by means of this index so far as important productive qualities of the Askania sheep is concerned, particularly the reproductive and growth performance of these animals.

With direct selection on liveweight at various ages of the sheep of the Karnobatska fine-wool breed a higher selection response is produced at 9 and 18 months than at weaning and at 2.5years (2.9 and 2.9as against 0.6and 1.2per cent) (Lazarov, 1981). This demonstrates the dependability of the definite selection based on live weight at the age of 18 months.

The response to selection on wool yield was investigated with sheep belong ing to the Dobrouja type of the Northeast Bulgarian fine-wool breed that were selected (25 per cent) directly on the weight of greasy wool or using the trait that was most strongly associated with it, and by one of the most effective selection indexes of 2, 3, 4, and 5 components of the fleece weight (Mihailova, 1983). The improvement per generation from direct selection (10.9 per cent) is almost twice as high as that recorded for selection using a correlated character (5.7per cent). Selection indices that include 2 to 4 characters produced similar effects on the amount of wool, but these constitute 68 to 72 per cent of the effects produced with direct selection on wool yield.

With the study on the parameters of the genetic effectiveness with sheep, belonging to the Shoumen type of the Northeast Bulgarian fine-wool breed the annual genetic progress from selection on wool yield was 3.04 per cent when 8 rams and 4 lines were used as against 0.60 per cent with the use of 24 – 30 rams and 6 lines (Stoyanov, 1980). This showed that it was very important to optimize the individual elements of selection work in order to obtain maximum genetic progress with each breed of sheep. In the working out of an optimized selection programme for the Askania breed (Hinkovski and Aleksiev, 1980) only 21 out of a total of 46,080 variants were determined as optimal from the genetic viewpoint.

In the scheme reflecting the results of the progeny testing of rams the highest annual genetic progress for wool yielding capacity (4.41 per cent) is obtained with the use of two rams only, i.e., when no genealogical structure of the population is maintained (Hinkovski and Alexsiev, 1980). The application of an optimal variant, envisaging the maintenance of six genealogical lines results in 4.05 per cent annual genetic progress in wool yield. Both variants contribute to the substantiation of an equal genetic progress by growth performance at the rate of 0.52per cent per year.

In the scheme reflecting the results of selection on performance test of rams at the age of 18 months with the maintenance of genealogic structure of six lines the maximum genetic progress obtained was 4.84 per cent with regard to wool yield, and 0.97 per cent with regard to growth capacity. The effectiveness of this variant is chiefly triggered by the shortening of the generation interval-from 4.08 to 2 years - as well as by the enhanced intensity of selection with the rams (8.3 vs 33.3 per cent). From testing on own phenotype, using no linear structure, the genetic progress with rams is lower (3.11per cent per year).

The practical use of optimized selection programmes with sheep in this country makes it necessary to perfect the system of selection and to adopt the machine processing of information for the elite part of each breed. Work has been initiated along these lines, referring to the implementation of some elements of the large-scale selection in sheep breeding, the application of the best linear unbiased production (BLUP) method in testing the breeding value of sheep and the working out of programmes to streamline the work associated with the retrieval, processing, and use of data. The building up and the practical application of such programmes will create conditions for the optimization of the selection process and for the enhancement of the genetic progress made in regard to the economically valuable traits with sheep.

TABLE 1. Wool yielding capacity of ewes at the ram producing flocks over the 1980–1984 period.

TABLE 2. Characteristics of the breeding rams at the age of 18 months (1984)

TABLE 3. Growth of lambs and utilization of food by fine-wool breeds

TABLE 4. Selection index (1 ) for testing the breeding sheep of the Askania breed
(after Ts. Hinkovski, 1971)

1₄= 2.736 x₁+ 0.204 x₂+ 0.076 x₃+ 1.147x₄+ 0.359 x₅+ 0.062 x₆+ 0.051 x₇